Since you are the SPOF in both of them you're not solving anything by having two, better to go all-in on a process that is bulletproof. If you have two processes they're compromising with one another.

Not to say you shouldn't have tiers as @DarthCoin rightly suggests, like cold, cache, and hot. I'm referring to the most important tier, your BIP39 tier example I would rationalize as cache and that's perfectly reasonable.

People (that should self-custody)

Political security is just as important to Bitcoin as the technical, even if Bitcoiners hate to admit it. Security is layered, and the technical layer is an enforcement arm of the political layer, but only if the technical layer is sufficiently distributed.

Political security is the only thing that prevents Google, Blackrock, Microsoft, Apple, the NSA, GCHQ, and god knows what other entities from stealing millions of coins... they have no purely technical blockers and having the majority of supply doesn't immunize them from the political fallout (and the technical resistance that could be brought with it.)

I think that's a fools errand, and that believing you can do so is hubris. Udi is right on this one, the best solution for 80% of people is either an ETF, Collaborative, equity in sats-flow, or a Family Office setup.

Everything I do with Lightning.Pub is part of a Family Office / Small Org vision of the future that keeps trust distributed to the edge and sats-flow as the gateway drug to that distribution.

Better tooling can get us from the 1-3% we should be at today to the ~20% I estimate is the (realistic) goal.

Even with better tooling custodians are going to be a major part of Bitcoin forever, the goal of such tooling shouldn't be to eliminate them but to keep them in a Mexican standoff by expanding the array of options people have.